Connecting 1 1/4 Tailpiece To 1 1/2 Drain: A Complete Guide

If you’re putting together a sink, you need the right pipes and adapters to do the job. Once you’ve figured that out, assembling your own kitchen drain is relatively easy. 

Most kitchen sinks have a 3 ½ inch drain opening with a 1 ½ inch drain opening. However, if you have an older or a smaller tailpiece, it’s like 1 ¼ inches instead of 1 ½. You can resolve this by simply purchasing a pipe reducer. 

1 ¼ to 1 ½: Is it Possible? 

The quick answer is, yes. A thread-in pipe adapter will cost you a few dollars at your local hardware store. You will, however, want to double check that your threaded pipe adapter fits into the drain. For this reason, it may be an idea to detach the strainer from your sink and bring it with you. 

Otherwise, making the connection between a 1 ½ inch drain and a 1 ¼ tailpiece is relatively easy. However, as that’s very rare, it’s also important to double check the measurements or check that you’re installing the right equipment into the right sink.

1 ½ Inch – A 1 ½ inch tailpiece is normally used for kitchen sinks. This wider pipe allows more water flow and is better if you want to leave the sink running while you wash dishes. It’s also less likely to become clogged if you rinse food down the drain. 

1 ¼ Inch – The 1 ¼ tailpiece is more common in bathrooms, such as bathroom sinks, showers, bathtubs, etc. In some cases, you’ll also find it on very old or very small double sinks, with the two 1 ¼ inch channels meeting in a 1 ½ or even 2-inch pipe that runs to the trap and to the wall. 

Essentially, if you’re fitting a 1 ¼ inch tailpiece to a 1 ½ drain, the tailpiece is too small. You want to consider if this is a route you really want to take. For example, it could increase the risk of your sink clogging. It might also increase the risk of your sink backing up and flooding when left running. 

Otherwise, it’s unlikely to actually cause a problem. So long as you have a strainer in place over the drain and the sink is only for light usage, you’ll be fine. However, it is not recommended. In addition, some local plumbing codes may expressly forbid using a 1 ¼ inch line with a kitchen sink. On the other hand, if you have a bathroom sink or a shower, it doesn’t matter. 

Finding the Right Sink Drain Piece Adapter 

Most sinks are sold with 1 ½ or 1 ¼ inch fittings for the tailpiece. The tailpiece is the part of the pipe that fits directly against the sink drain in the basin, usually screwing onto a strainer or a threaded pipe built into the sink. However, it may simply slot on and you may have to rely on gravity or pipe cement to hold the pipe in place. Here, different pipe sizes are normally used for different types of sinks. 

You’ll have to check the size and type of your drain outlet to determine which type of fitting to buy. If you’re completely lost, simply take the strainer with you – unless it screws fully into the sink. Chances are, you’ll need a straight 1 ½ inch to a 1 ¼ inch reducer, with threading to match that on the drain (usually internal on the reducer). Here, you always want a “reducer” because these are designed to direct pressure downwards into the smaller pipe. An adapter might not have the right interior to direct water downwards, which might result in a higher chance of leakage. 

How to Connect 1 ¼ Sink Drain to 1 ½ P-Trap: 5 Easy Steps 

If you’re connecting a 1 ¼ inch sink drain to a 1 ½ inch P-trap, the process is easier and more likely to meet local building codes. However, you still have to check if you’re actually legally allowed to work on your own plumbing in your area. 

Decide Where to Place the Adaptor

Chances are, you want to put your adaptor just after the tailpiece, not before it. That will make the installation process significantly easier. However, you may also choose to put your adaptor in at any point before the P-trap. Your choice should depend on what pipes you have laying around, how much space you have under your sink, and accessibility. 

The easiest place to install the adapter is between the tailpiece and the trap as there are specialty trap adaptors sold for just this reason. 

Buy an Adaptor 

You should buy a Schedule 40 PVC trap adaptor or pipe adaptor. If your drain uses ABC, buy that instead. However, your adapter should always be 1 ¼ inches to 1 ½ inches. Make sure you’re buying an adapter and not a reducer. Here, you also want to check if you want an angled adaptor. A straight adapter is easiest to install and is perfect if your pipe continues straight afterwards. On the other hand, if you want an angled connection, you may choose an angled adaptor – or simply install the adapter after an elbow. 

Cut the Pipe 

The pipe has to cover the distance between the drain and the P-Trap in whatever configuration you cut it to. That distance also now has to include the adapter. In most cases, adapters can be as small as 1/8th of an inch when installed. In others, they might cover some distance. It’s important to cut your pipe to fit the adapter after you buy it because a good fit depends on which adapter you buy. 

Insert the Adapter 

Insert your adapter and attach the P-trap. Depending on your setup, this might require threading the pipe into place with P.T.F.E. tape. In other cases, you might want to permanently seal connections with PVC cement. It’s important that the full system can be taken apart. Otherwise, you’ll have difficulty cleaning the P-Trap in case it clogs. 

Double Check for Stress Leaks 

Run water down your drain to ensure that everything is draining properly. If you have any leaks, adjust the threads, add PVC cement, or change the layout of the drain to prevent leaks. 

What Size PVC Pipe is Best for Sink Drain? 

That depends on what type of sink you have. Most areas require a 1 ½ inch drain pipe for kitchen sinks. However, you can easily use a 1 ¼ inch drain pipe for bathroom sinks, bathtubs, and showers. However, if you have a very high-pressure shower, you might prefer to use the larger drainpipe. Why? Water will drain faster. That also means you’re less likely to have a clog or water backing up. 

That can be very important if you have a lot of water pressure, several shower heads, or another reason why you might have extra water going down the drain. In addition, you almost always want a larger downpipe for a high-use sink. The more you use the sink, the more likely it is to become clogged or to back up with a smaller drain in place. So, if you’re installing a sink in a workshop and intend to use it heavily, make sure you use the larger drain. 

Related Questions 

If you still have questions, this FAQ might help. Otherwise, feel free to ask a specific question in the comments for custom advice. 

Can I use a 1 ½ inch P-Trap for Bathroom Sink? 

Yes. Just install a P-trap adapter to ensure that the plumbing fits together. In most cases, you’ll have to adapt the drain up anyway. For example, most wall drain pipes are 2 inches. In this case, you’ll just have to spend a few extra dollars on an extra adapter.           

Are All Bathroom Sink Stoppers the Same Size? 

Unfortunately, no. Bathroom sinks use several standardized sizes, but they are not all the same. For example, the most common size is 1 ½ inches. Most bathroom drain stoppers are in this size. However, you might also have a sink that needs a 1 ¼ inch stopper or even a 1 5/8ths stopper. It’s always a good idea to measure the drain before buying a stopper. 

What’s a Trap Adaptor? 

A trap adaptor resizes the pipe to the size of the P-Trap it is connecting to. It may also provide a threaded point to screw the P-trap into, so you can glue the adapter to the pipe for more durable plumbing. The adaptor is normally small and fits between the P-Trap and the drain tailpiece. It can also go from 1 ½ to 1 ¼. However, you’re unlikely to find a 1 ¼ to 1 ½ adaptor specifically for your P-Trap. 


Installing adapters and reducers into your sink plumbing is easy. However, you should always check that you’re allowed to do so. It’s also important to double check that your installation won’t cause problems such as your sink backing up. When in doubt, always get professional advice.

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